Speed Made to Wait until Friday

The Formula One team had hoped to make a decision after a test at Silverstone on Wednesday but bad weather prevented the Californian from setting a time or doing more than one lap.

With regular race driver David Coulthard and Italian Vitantonio Liuzzi due to test on Thursday, Red Bull said they hoped to get Speed back in the car on Friday before making their choice.

Formula One has not had a US driver since Michael Andretti in 1993. While Speed would be taking part only in Friday practice, it would give the crowd at Indianapolis some local interest for the June 19 race.

The teams that finished fifth or lower in last year's Championship are allowed to run an extra car in Friday practice sessions before race weekends.

Red Bull have alternated Liuzzi and Austrian Christian Klien in the third driver role, with both drivers also taking turns in the second race car over the last seven Grands Prix.

Klien is due to race alongside Coulthard in Canada after Liuzzi competed in the last four.